JPH0344457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an emitter-coupled astable multivibrator used, for example, in an integrated circuit FM modulator.

[Technical background of the invention and its problems]

FIG. 1 is a circuit diagram of a conventional emitter-coupled unstable multivibrator 90. Note that the portion surrounded by a broken line indicates the bias circuit 28. This bias circuit 28 is a bias circuit that does not perform temperature compensation, and resistors 14 and 15
It consists of a series circuit formed by connecting these in series. Resistor 14 is connected to the power supply voltage Vcc, and resistor 1
5 is grounded. Further, the bias voltage output terminal 27 is provided at the midpoint between the resistors 14 and 15.

The circuit configuration of multivibrator 90 will be explained below. The collectors of the pair of transistors 1 and 2 are connected to the emitters of transistors 3 and 4, respectively. Further, the collector of the transistor 1 is also connected to the emitter of the transistor 5 via a resistor 12, and the collector of the transistor 2 is connected via a resistor 13. Furthermore, the collector of transistor 1 is connected to the base of transistor 6.
It is connected to the base of transistor 2 via an emitter coupling, and is also connected to the base of transistor 8, and the collector of transistor 2 is connected to
It is connected to the base of transistor 1 via the base-emitter connection of transistor 7, and also to the base of transistor 9.

The bases of the transistors 3 and 4 are both connected to the output terminal 27 of the bias circuit 28,
The collector is connected to power supply voltage Vcc. Further, the base and collector of the transistor 5 and the collectors of the transistors 6, 7, 8, and 9 are also connected to the power supply voltage Vcc. The emitter of the transistor 6 is connected to the base of the transistor 2 as described above, but is also branched off and grounded via the resistor 24. Similarly, the emitter of transistor 7 is also branched and grounded via resistor 25. In addition, transistors 8 and 9
The emitters of are connected to the bases of transistors 10 and 11 via resistors 20 and 22, respectively. The bases of the transistors 10 and 11 are grounded through resistors 21 and 23, respectively, and the emitters are coupled together and grounded through a current source 17. Further, the collectors of the transistors 10 and 11 are connected to the emitters of the transistors 1 and 2, respectively, and the emitters of the transistors 1 and 2 are coupled to each other via a capacitor 16.

Now, multivibrator 9 with the above configuration
The operation of 0 will be explained with reference to the signal waveform diagram in FIG. In the following, changes over time in collector potentials V _C1 and V _C2 and emitter potentials V _E1 and V _E2 of transistors 1 and 2 will be followed.

The oscillation operation of the multivibrator 90 is performed by repeatedly turning transistors 1 and 2 on and off alternately. First, at time _t1 , transistor 1 is turned on and transistor 2 is turned off. Suppose. At this time transistor 3
is also ON, the collector potential V _C1 of transistor 1 is the output terminal 2 of the bias circuit 28.
The potential is lower than the potential of transistor 7 by the base-emitter voltage _VBE3 of transistor 3. Output terminal 2
7 and the power supply voltage Vcc is _V0 , the potential of the output terminal 27 is Vcc- _V0 , so the collector potential _Vc1 of the transistor ₁ at time t1 is _Vc1 = Vcc- _V0- V _BE3 (t=t ₁ ). In addition, since transistor 2 is turned off, the collector potential V _c2 of transistor 2 is lower than the power supply voltage Vcc by the base-emitter voltage V _BE5 of transistor 5, and V _c2 = Vcc - V. It is expressed as _BE5 (t=t ₁ ).

Next, consider the emitter potentials V _E1 and V _E2 of transistors 1 and 2 at time t ₁ . Here, the voltage between the base and emitter of transistor 7 is V _BE7 , and the voltage between the base and emitter of transistor 1 in the ON state is V BE7.
If V _BE1 , then V _E1 =Vcc-V _BE5 -V _BE7 -V _BE1 (t= _t1 ). Now, since the transistor 1 is turned on, the transistor 11 is also turned on, and a constant current _I0 flows through the capacitor 16 as shown by the solid arrow in FIG. As a result, capacitor 16
is charged at a constant speed with the polarity in the direction of the solid arrow, and as a result, the emitter potential of transistor 2 increases.
As shown in FIG. 4d, V _E2 decreases at a constant speed after time _t1 . And the emitter potential
V _E2 continues to decrease and when the base-emitter voltage V _BE2 of transistor 2 reaches a certain value, the state of transistor 2 is reversed from ON to OFF.
The value of the emitter voltage V _BE2 that causes this inversion is V _BE2
(ON) and the time of inversion is t ₂ , then time t ₂
The emitter potential V _E2 of the transistor 2 at is V _E2 = V _B2 − V _BE2 (ON) (t=t ₂ ). Here, V _B2 is the base potential of transistor 2, and V _B2 is the collector potential of transistor 1.
Since the base-emitter voltage V _BE6 of transistor 6 is lower than V _c1 , it is expressed as V _B2 = V _c1 − V _BE6 = Vcc − V ₀ − V _BE3 − V _BE6 , and as a result, V _E2 = Vcc − V ₀ −V _BE3 −V _BE6 −V _BE2 (ON
)(t=t ₂ ).

When transistor 2 is reversed from OFF to ON,
Transistor 1 is inverted from ON to OFF. Therefore, this time the collector potential of transistor 1
V _c1 becomes V _c1 = Vcc - V _BE5 (t = t ₂ ), and the collector potential V _c2 of transistor 2 becomes V _c2 = Vcc - V ₀ - V _BE4 (t = t ₂ ). Then, the emitter potential V _E2 of the transistor 2 turned ON at time t 2 is similar to the emitter potential V _E1 of _the transistor 2 at time t ₁ , V _E2 = Vcc − V _BE5 − V _BE6 − V _BE2 (t = _t2 ). Here, V _BE2 represents the base-emitter voltage of transistor 2 in the ON state.

Now, at time _t2 , the emitter potential V _E2 of transistor 2 is subtracted from Vcc-V ₀ -V _BE3 -V _BE6 -V _BE2 (ON) to Vcc-V _BE5 -V _BE6 -V _BE2 by subtracting V ₀ +V _BE3 −V _BE5 +V _BE2 (ON) −V _BE2 is increasing. Here, the resistor 12 is selected so that when the transistor 3 is in the ON state, the currents flowing through the collectors of the transistors 3 and 5 are equal, and the base-emitter voltage V _BE3 of the transistor 3 and the base of the transistor 5 are equal.・The emitter voltage V _BE5 is equal. But then,
The increase in the emitter voltage V _E2 of transistor ₂ at the previous time t 2 V ₀ +V _BE3 −V _BE5 +V _BE2 (ON)−V _BE2 is, since V _BE3 = V _BE5 , V ₀ +V _BE2 (ON)− V _BE2 . As a result, the emitter voltage V _E1 of transistor 1 at time t ₂ becomes a potential higher than Vcc − V _BE5 − V _BE7 − V _BE1 at time t ₂ by the above increase, V _E1 = Vcc − V _BE5 − V _BE7 −V _BE1 +V ₀ +V _BE2 (ON)
It can be seen that -V _BE2 (t=t ₂ ).

After time _t2 , when transistor 1 is OFF and transistor 2 is ON, a constant current I ₀ flows in the direction of the dashed arrow in _FIG . As shown in Figure c, it decreases at a constant speed. Then, if the base-emitter voltage required for transistor 1 to turn from OFF to ON is V _BE1 (ON), then V _E1 = Vcc - V ₀ - V _BE4 - V _BE7 - V _B
At the time when _E1 (ON) is reached (time t ₃ ), transistor 1 is turned on again.
turns on and transistor 2 turns off.
Emitter voltage of transistor 1 in ON state
V _E1 returns to V _E1 = Vcc − V _BE5 − _{V BE7} − V _BE1 (t=t ₈ ), and the increase in V _E1 at time t ₃ is V ₀ + V _BE4 − V _BE5 + V _BE1 (ON) −V _BE1 . As before, the value of the resistor 13 is selected so that the base-emitter voltages V _BE4 and V _BE5 of transistors 4 and 5 are both equal, so the increase in V _E1 at time _t3 ends up being becomes V ₀ + V _BE1 (ON) − V _BE1 . From this, the emitter voltage V _E2 of transistor 2 at time t ₃ is higher than Vcc + V _BE5 − V _BE6 − V _BE2 before time t ₃ by the above increase, V _E2 = Vcc − V _BE5 − V _BE6 −V _BE2 +V ₀ +V _BE1 (ON)
−V _BE1 (t=t ₃ ).

After that, transistors 1 and 2 are repeatedly turned ON and OFF, and the collector potential of transistor 1 increases.
V _c1 or collector potential of transistor 2 V _c2
As shown in FIGS. 4a and 4b, the pulse waveforms are repeated at a constant period of 2T, and the oscillation output of the multivibrator 90 is obtained. In this case, due to the change in the collector potential V _c1 of the transistor 1 during the period T, the terminal voltage of the capacitor 16 changes from Vcc − V ₀ −V _BE4 −V _BE7 −V _BE1 (ON) to Vcc−V _BE5 − during the period T. V _BE7 −V _BE1 +V ₀ +V _BE2
(ON) – V _BE2 , changes by 2V ₀ +V _BE1 (ON) – V _BE1 – V _BE2 (ON) – V _BE2 . By choosing transistors 1 and 2 symmetrically, V _BE1 = V _BE2 and V _BE1 (ON) = V _BE2 (ON), so the change in the voltage applied to the capacitor 16 is 2 (V ₀ + V _BE1 (ON) ) − V _BE1 ). Therefore, the capacitance of the capacitor 16 is C
Then, C・2(V ₀ +V _BE1 (ON)−V _BE1 )=I ₀・T holds true, and therefore, the oscillation frequency ₀ of the multivibrator 90 is ₀ = 1/2T=I ₀ /4CVc... …(1) is found. Here, V ₀ is the voltage of transistors 1 and 2.
The terminal voltage of the capacitor 16 when ON and OFF are reversed is expressed as Vc = V ₀ + V _BE2 (ON) + V _BE1 (2).

From the above equation (1), it can be seen that the oscillation frequency ₀ changes by changing the constant current I ₀ . Therefore, by using the video signal as an input signal and changing the constant current I ₀ in phase with this input signal,
Multivibrator 90 can be used as an FM modulator in a VTR.

Now, the oscillation frequency ₀ of this emitter-coupled unstable multivibrator 90 has a temperature drift, which will be explained in detail below.

The reason why the oscillation frequency ₀ has a temperature drift is
The terminal voltage of the capacitor 16 shown by the above equation (2)
This is because Vc has a temperature drift. That is, for example, at time t ₂ when transistor 2 is reversed from OFF to ON, the collector currents of transistors 1 and 2 are not actually equal, so that the emitter-base voltage of transistors 1 and 2 at time t ₂ is V A difference occurs in the temperature coefficients of _BE1 and V _BE2 (ON), and the terminal voltage Vc has a temperature drift.

To understand this in more detail, the collector current I _c2 flowing through transistor ₂ at time t 2
Consider (ON). Now, assume that the emitter potential V _E2 decreases by ΔV before time t ₂ when the transistor 2 is in the OFF state. At this time, the current flowing through the resistor 13 increases by ΔV·g _{n2, where g n2 is} the mutual conductance of the transistor 2.
As a result, the collector potential of transistor 2 V _c2
decreases by △V・g _n2・R ₁₃ . This collector potential
The change in V _c2 passes through the base-emitter junctions of transistor 7 and transistor 1, the capacitor 16 in sequence, and is fed back directly to the emitter of transistor 2 itself. Transistor 2 goes from OFF to ON
The condition for reversing is the loop gain G at this time,
That is, G=ΔV·g _n2 ·R ₁₃ /ΔV=g _n2 ·R ₁₃ (3) is one or more. Therefore, G=
At the moment when it becomes 1 (time t ₂ ), transistor 2 becomes
Flip from OFF to ON. The collector current of the transistor 2 at this moment is I _c2 (ON), and the mutual inductance g _n2 is expressed as g _n2 = g/kT·I _c2 (ON) (4). Here, k is Boltzmann's constant, T
is the absolute temperature, and g is the unit charge. From the above equations (10) and (11), the collector current I _c2 (ON) of the transistor 2 at the time of inversion is determined as I _c2 (ON)=kT/g·R ₁₃ (5).

Now, as described above, since the collector current I _c2 (ON) has been found, the base-emitter voltage V _BE2 (ON) of transistor 2 at the time of inversion can be calculated _by , V _BE2 (ON) = kT/glnI _c2 (ON)/I _s = k
t/glnkT/I _s・gR ₁₃ ...(6) is found. Also, transistor 1 at the time of inversion
The base-emitter voltage V _BE1 of transistor 1 is
Since the collector current I _c1 of is equal to I ₀ , V _BE1 = kT/glnI ₀ /I _s (7). Therefore, from Equations (6), (7), and Equation (2) above, the terminal voltage V _c of the capacitor 16 at the time of inversion is Vc = V ₀ -kT/glngR ₁₃ I ₀ /kT... …(8) is obtained. This revealed that the terminal voltage Vc is a function of the temperature T and has a negative temperature drift. Therefore, the oscillation frequency ₀ expressed by equation (1) has a positive temperature drift.

[Purpose of the invention]

The present invention has been made in view of the above problems, and an object of the present invention is to improve the temperature characteristics of the oscillation frequency of this emitter-coupled unstable multivibrator.

[Summary of the invention]

The present invention allows the voltage V ₀ applied to the resistor 14 of the bias circuit 28 to have a temperature drift opposite to that of the terminal voltage V ₀ of the capacitor 16, thereby canceling out the temperature drift of Vc, and thereby oscillating. This is an emitter-coupled unstable multivibrator that successfully eliminates temperature drift at _zero frequency.

[Example of the present invention]

An embodiment of the present invention will be described below with reference to FIG. Multivibrator 100 shown in FIG.
However, the difference from the multivibrator 90 shown in FIG. 1 is as follows.

In the multivibrator 100 of FIG. 3, the output terminal 27 of the bias circuit 28 is connected to the bases of the transistors 3 and 4 via the base-emitter junction of the transistor 31. Similarly power supply Vcc
is connected to the base of transistor 5 via the base-emitter junction of transistor 30.
The emitter of transistor 30 is connected to ground via resistor 32, and the emitter of transistor 31 is connected to ground via resistor 33. Resistors 32 and 33 can generally be replaced with constant current sources.

If the difference between the emitter voltages of the transistors 30 and 31 is V ₁ , the voltage applied across the resistor 14 is V ₀ , so V ₁ can be written as equation (9): V ₁ = V ₀ − V _BE30 +V _BE31 ...(9) Here, if the collector currents flowing through transistors 30 and 31 are I _c30 and I _c31 , then V _BE30 = kT/glnI _c30 /I _s30 ...(10) V _BE31 = kT/glnI _c31 /I _s31 ...(11) Here, I _s30 and I _s31 are the saturation currents of the transistors 30 and 31.

According to equations (9), (10), and (11), V ₁ =V ₀ −kT/glnI _c30 /I _s30 +kT/glnI _c
31 /I _s31 =V ₀ −kT/glnI _c30 /I _c31 I _s31 /I _s30 ……(12
) becomes.

Here, by substituting V ₁ for V ₀ in equation (8), the terminal voltage of capacitor 16 at the time of inversion in the circuit of Figure 3 is
Find Vc. Vc is, Vc=V ₀ −kT/gInI _s31 /I _s31 −kT/glnI ₀ /I _c
2 (ON) = V ₀ -kT/glnI _s31 /I _s30 I _c30 /I _c31 I ₀ /I _c2 (
ON) =V ₀ −kT/glnI _s31 /I _c31 I _c30 /I _c31 gR ₁₃ I ₀
/kT……(13) Here, when Vc is differentiated by T, ∂Vc/∂T=−k/g(lnI _s31 /I _s30 I _c30 /I _c31 gR ₁₃ I ₀
/kT−1) ...(14) At temperature T=T ₀ , the following equation (15) should be satisfied to make ∂Vc/∂T=0 I _s31 /I _s31 I _c30 /I _c31 gR ₁₃ I ₀ /kT ₀ = e……(15
) Here e is the base of the natural logarithm.

From the above, I _s31 /I _s30・I _c30 satisfies formula (15)
/I _c31 , that is, resistors 32, 33
By determining the emitter area ratio of the transistors 30 and 31, the temperature drift of Vc can be made zero at T= _T0 . In other words, it is possible to compensate for temperature drift at an oscillation frequency of ₀ .

[Other embodiments of the present invention]

Another embodiment of the present invention will be described below with reference to FIG.

In the multivibrator 200 shown in FIG. 4, the output terminal 27 of the bias circuit 28 is connected to the collector of the transistor 40 via the resistor 15, the emitter of the transistor 40 is connected to ground, and the base thereof is connected to the resistor 40.
2 to ground. Further, the collector of the transistor 40 is connected to the base via a resistor 41.

Since the base-emitter voltage V _BE40 of the transistor 40 is applied to the resistor 42, the current flowing through the resistor 42 is V _BE40 / _R42 . Therefore, if the base current of the transistor 40 is negligibly small compared to this current, it can be considered that the same current as the resistor 42 is flowing through the resistor 41, and the output terminal 2
7 voltage V ₂₇ is as shown in equation (20) V ₂₇ = R ₄₂ + R ₄₁ / R ₄₂ V _BE40 ... (20) Here, if we set R ₄₂ + R ₄₁ / R ₄₂ = χ, then resistor 14 If this voltage is V ₂ , then V ₂ = (Vcc−χV _BE40 ) R ₁₄ /R ₁₄ +R ₁₅ (21). At this time, differentiating V _re ' with respect to temperature T gives ∂V ₂ /∂T=−χR ₁₄ /R ₁₄ +R ₁₅ ∂V _BE40 /∂T...
(22) becomes.

Further, Vc can be expressed as Vc=V ₂ −kT/gln(gR ₁₃ I ₀ /kT) (23) where V ₀ is V ₂ in equation (8).

Here, when V ₀ is differentiated with respect to temperature T, ∂Vc/∂T=∂V ₂ /∂T−k/g(lngR ₁₃ I ₀ /kT−1) ……(24) Substituting (22) into equation (24) Substitute ∂Vc／∂T=−χR ₁₄ ／R ₁₄ ＋R ₁₅ ∂V _BE4
0 /∂T−k/g(lngR ₁₃ I ₀ /kT−1)……(25) Here, from equation (21), R ₁₄ /R ₁₄ +R ₁₅ =V ₂ /Vcc−χV _BE40 ……(26) Therefore, at T=T ₀ , equation (25) is (∂Vc/∂T) _T=T0 = χV ₂ /Vcc−χV _BE40 ∂V
_BE40 /∂T−k/g(lngR ₁₃ I ₀ /kT−1)……(27) It can be written. Therefore, by setting (∂Vc/∂T) _T=T0 = 0, χ can be found, that is, R ₄₁ and R ₄₂
Find the ratio of Furthermore, by determining the current flowing through the resistors 4 and 42 and the transistor 40,
The values of resistors 41 and 42 are determined. Furthermore, the values of resistors 14 and 15 can also be determined from equation (26).

As described above, with the circuit shown in FIG. 3, the temperature drift of Vc becomes 0 at temperature T=T ₀ . In other words, it is possible to compensate for temperature drift at an oscillation frequency of ₀ .

〔Effect of the invention〕

Next, the effects of the present invention will be specifically shown. In Figure 1, resistors 12 and 13 are 1.6KΩ, resistors 14 and 15 are 500Ω and 6KΩ, respectively, resistors 20 and 22 are 5.3KΩ,
Resistors 21 and 23 are 6KΩ, capacitor 16 is 120PF
FIG. 5a shows the relationship between temperature and oscillation frequency when the current source 17 is 720 μA.

Further, FIG. 5b shows the relationship between the temperature and the oscillation frequency of the circuit shown in FIG. 3, which is subjected to the temperature compensation of the present invention. Here, resistors 14 and 15 are 500Ω and 6.08KΩ, resistors 32 and 33 are 27KΩ and 6KΩ, and the emitter area ratio of transistors 30 and 31 is 4:1, so that ∂Vc/∂T=0 at T=27°C. It is designed to.

As is clear from FIG. 5, the variation in the oscillation frequency is suppressed to 10 KHz in the temperature range of 0°C to 100°C. When compared with the case without temperature compensation, it can be seen that the temperature drift is clearly improved.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional emitter-coupled unstable multivibrator, Figure 2 is a waveform diagram for explaining its operation, and Figure 3 is an emitter-coupled unstable multivibrator with temperature compensation according to the present invention. FIG. 4 is a block diagram showing another embodiment of the emitter-coupled multivibrator with temperature compensation of the present invention, and FIG. 5 is a block diagram of a conventional emitter-coupled non-stable multivibrator. FIG. 4 is a diagram showing the relationship between temperature and oscillation frequency in the vibrator and the emitter-coupled unstable multivibrator of the embodiment of the present invention shown in FIG. 3; 1 to 11...Transistor, 12,13...Resistor, 16...Capacitor.

Claims (1)

[Claims] 1 first and second transistors with a capacitor connected between their emitters, third and fourth transistors forming a current source, and fifth, sixth, and seventh transistors with collectors connected to a power supply. the emitters of the first and second transistors are connected to the collectors of the third and fourth transistors, respectively, and the collectors of the first transistor are connected to the bases of the second and third transistors; Further, the collector of the second transistor is connected to the bases of the first and fourth transistors to form a feedback loop, and the collector of the first and second transistor is connected to the base of the fifth transistor through a resistor, respectively. and the collectors of the first and second transistors are connected to the emitters of the sixth and seventh transistors, respectively. An emitter-coupled unstable multivibrator comprising a bias circuit having a positive temperature drift connected between the bases of the fifth transistor and the base potential of the fifth transistor.